P.J. Hogan, director of “My Best Friend’s Wedding,” returns to the Australian film industry for the first time since his 1994 film “Muriel’s Wedding,” launching Toni Collette’s career. Collette reunites with Hogan nearly 20 years on for the smart, funny but ultimately chaotic film “Mental.”

The story revolves around Shirley Moochmore (Rebecca Gibney), a mother of five young girls, who longs for her family life to be more like that of the Von Trapps from “The Sound of Music.” Barry Moochmore (Anthony LaPaglia) is too busy running a re-election campaign for mayor of the fictional Australian town of Dolphin Heads to notice that his wife has been driven crazy by his absence and by the girls, each of whom thinks she has a mental disorder of her own.

After a particularly bad (yet musical) psychotic episode, Shirley is sent off “on holiday to Wollongong” (read: institutionalized at a local asylum). With Shirley gone, Barry is left to parent his five daughters.

The film is semi-autobiographical: Hogan’s mother had a mental breakdown when he was a child, and his father kept it a secret to protect his campaign. Hogan’s father also picked up a hitchhiker to babysit the children.

The film is over-the-top and chaotic, which adds to its charm, but some unwanted chaos arises directly from Hogan’s screenplay. Romance, slapstick and drama don’t flow well from scene to scene. Shaz confronts Barry about his paternal negligence in an emotional scene of reconciliation; shortly after that, Barry calls the cops on Shaz and chases her out of the house.

Hogan occasionally fails to convey details of his childhood story, leaving strange gaps. For instance, when Barry picks up Shaz, there's no discussion about the terms of her employment or judgment of her character. One minute, she’s hitchhiking on the side of the road, and the next, she’s a live-in nanny in charge of a stranger’s children.

The film is full of smart, inventive humor, but it's not without some silly low-brow gags that bring down the otherwise insightful, entertaining look at mental health issues.

What the film lacks in cohesive sequences, it makes up for in strong performances, particularly from Collette. Her over-the-top portrayal of Shaz is full of energy and attitude as she instills self-esteem in the girls, showing them that everyone is crazy in her own right and normality is relative.

The film is at its best when focusing on the coming-of-age of the oldest Moochmoore daughter, 16-year-old Coral (Lily Sullivan). Sullivan effectively captures the insecurities of adolescence, a time in life when everyone thinks she’s crazy, regardless if she's an Australian being babysat by the anti-Mary Poppins.

Liev Schreiber (“Manchurian Candidate,” “X-Men Origins: Wolverine”) plays Trevor Blundell, Coral’s shark-hunter boss who has a connection with Shaz. Schreiber’s natural intensity transfers well into this crazed environment and, even though he is one of the more grounded characters, his stability elicits many laughs.

At one point, Shirley says, from within the mental institution, “I can’t tell whether everything is coming together or falling apart.”

That sentiment perfectly sums up the theme and production of “Mental.”